首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   472篇
  免费   23篇
  国内免费   81篇
化学   353篇
晶体学   2篇
力学   54篇
综合类   5篇
数学   7篇
物理学   155篇
  2023年   1篇
  2022年   13篇
  2021年   19篇
  2020年   13篇
  2019年   11篇
  2018年   16篇
  2017年   11篇
  2016年   12篇
  2015年   16篇
  2014年   20篇
  2013年   27篇
  2012年   35篇
  2011年   25篇
  2010年   28篇
  2009年   28篇
  2008年   22篇
  2007年   39篇
  2006年   35篇
  2005年   30篇
  2004年   27篇
  2003年   22篇
  2002年   13篇
  2001年   13篇
  2000年   12篇
  1999年   7篇
  1998年   13篇
  1997年   16篇
  1996年   8篇
  1995年   7篇
  1994年   7篇
  1993年   3篇
  1992年   7篇
  1991年   1篇
  1990年   2篇
  1989年   6篇
  1988年   4篇
  1984年   2篇
  1983年   4篇
  1982年   1篇
排序方式: 共有576条查询结果,搜索用时 0 毫秒
171.
水平井蒸汽辅助重力驱油藏模拟方法   总被引:10,自引:0,他引:10  
研究了油藏与水平井段耦合的蒸汽辅助重力驱整体模拟的数学模型及其求解方法.将研制的沿水平井井筒方向有质量、能量损失的一维多相管流模块与油藏模拟主体软件集成,能预测水平井蒸汽辅助重力驱蒸汽腔室的大小及形状的动态变化.通过模拟计算分析了毛管力、蒸汽干度、地层深度等对蒸汽腔室发育程度的影响,并取得了结果.  相似文献   
172.
注蒸汽井井筒内参数计算新模型   总被引:11,自引:0,他引:11  
从动量定理角度出发建立求解蒸汽压降方程,而从能量守恒角度出发建立求解蒸汽干度变化的方程,采用节点分析方法和数值计算方法对模型求解.计算过程中借鉴传统的气液两相流Beggs-Brill方法计算水蒸汽混合物的物性参数.通过对辽河油田齐40块和杜80块10口井井筒的压力、温度和干度分布计算表明该模型计算精度较高.  相似文献   
173.
对一种商品蒸汽驱油用高温发泡剂HTFA样品用乙酸丁酯进行萃取分离和提纯,然后对分离组分分别进行了化学分析,红外光谱分析、元素分析、核磁共振谱分析及X射线衍射分析等多种性能及结构表征实验。推断出其组份是以油溶性乳化剂烷氧基聚氧乙烯基 磺酸钠为主要成份。与水溶性助乳化剂甲基丙烯酸钠、碳酸钠、硫酸钠等复配、乳化而成。结合各组份元素定量分析结果,推断其组成比全炙主乳化剂约占乳液总重量的8%~9%,助乳化剂  相似文献   
174.
  1. Download : Download high-res image (53KB)
  2. Download : Download full-size image
  相似文献   
175.
大型汽轮机部件低周疲劳安全寿命的设计和评定   总被引:1,自引:0,他引:1  
文中提出了汽轮机部件低周疲劳安全寿命的设计和评定方法。介绍了汽轮机部件低周疲劳安全寿命的含义和计算方法。该方法以概率论和统计学为基础,把汽轮机部件的低周疲劳寿命处理为随机变量,对低周疲劳试验数据进行统计分析来确定材料低周疲劳寿命的分布参数,使用可靠性理论来确定汽轮机部件的低周疲劳安全寿命。文中给出了低周疲劳寿命服从正态分布和对数正态分布时汽轮机部件低周疲劳安全寿命的计算方法和应用实例。该方法考虑了汽轮机运行参数随机性和材料低周疲劳特性离散性的影响,为汽轮机部件低周疲劳寿命的设计、评定和诊断提供了科学的依据。  相似文献   
176.
This paper presents a method and describes an experimental device for determining the steam-water relative permeabilites of unconsolidated porous media. The experimental conditions are as close as possible to those of geothermal reservoirs. The relative permeabilities have been obtained at 180 and 150?C. Their variations versus liquid saturation are quite classical. The air-water relative permeabilities have been measured also at room temperature. The values obtained under these three conditions are almost identical. However, the air-water relative permeability differs slightly from that of steam at 180 and 150?C. We think this discrepancy is acceptable in practice, as it is easier to determine the relative permeabilities for an air-water flow at room temperature than for a steam-water flow at high temperature and pressure.  相似文献   
177.
Conventional compression-refrigeration systems not only consume a large amount of electric power, but also cause serious environmental pollution. Among the various possible approaches in overcoming these two problems, a steam-ejector refrigeration system is believed to be most effective. This paper experimentally investigates the controlling parameters of a steam ejector, including operating conditions and the exit Mach number of the primary nozzle. Operation maps useful to the practical design are constructed from experimental results, and the empirical equations are correspondingly derived. Excessively increasing the exit Mach number of primary nozzle is unnecessary, and 4.35 should be a moderate value. With regard to the performance characteristics of the ejector itself, a steam ejector is better than an R114 ejector and is comparable to an R113 ejector. Moreover, with the use of a two-stage ejector, the required pressure to drive a steam ejector is reduced, and the low-grade heat source can be efficiently used. The results of primitive observation of the flow field are also discussed in this work.  相似文献   
178.
A convenient experimental method for measuring the thermal conductivity of uranin (fluorecein sodium, C20H10O5Na2) is described. Two similar blocks of uranin, produced from a strong uranin/water solution, were exposed to one-dimensional steady-state conduction. It was found that, for a mean bulk temperature ranging from ambient up to 55°C, the uranin has a constant thermal conductivity of 0.43 W/mK. Above these temperatures, the material begins to soften and the thermal conductivity is seen to decrease  相似文献   
179.
The plane one-dimensional and radially symmetric problems of injection of superheated steam into a porous medium saturated with gas are considered. Self-similar solutions are constructed on the assumption that in this case four zones are formed in the porous medium, namely, a gas flow zone, superheated and wet steam zones, and a water slug zone formed due to steam condensation. On the basis of the solution obtained, both the effects of the boundary pressure, mass flow rate, and temperature of the injected superheated steam and the effect of the initial state of the porous medium on the propagation of the hydrodynamic and thermal fields in the porous medium are studied.  相似文献   
180.
We formulate conservation laws governing steam and nitrogen injection in a one-dimensional porous medium containing water. Compressibility, heat conductivity and capillarity are neglected. We study the condensation front and shock waves arising in the flow. We find that there are four possible types of solutions for the initial and boundary conditions of interest. We describe a simple construction in the temperature saturation plane that determines the complete solution for the given conditions. Applications of the theory developed here are in clean up of soil contaminated with nonaqueous phase liquids. We show that a substantial cold gaseous zone develops in all solutions of practical interest, thus counteracting downward migration of the pollutant.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号